There is already a Glossodoris cincta https://www.inaturalist.org/taxa/126093-Glossodoris-cincta

?? It depends what on earth cf cincta means: is it a new species resembling cincta - in which case it should be identified to genus ...

I think it should be swapped but am open to other suggestions. WoRMS refers to the article above in their sources to Glossodoris cincta. http://www.marinespecies.org/aphia.php?p=taxdetails&id=214506

OK. the situation is simply that all the "cryptic" species were cryptic under colour variations, but with DNA colour differences are detectable, and in many cases current species can be identified from colour and shape, despite this being missed in the past.
So adding a complex on iNaturalist is superfluous.

https://www.biotaxa.org/Zootaxa/article/view/zootaxa.4444.5.1/33989

"The doubt as to whether this species represents the true Glossodoris cincta stems from the fact that the type locality for G. cincta is Mauritius. It is important to note that we were unable to obtain specimens of G. cincta from Mauritius (type locality). We noted that none of the color patterns of any of the cryptic and pseudocryptic species in the Glossodoris cincta species complex studied here matched the original plate figured by Bergh (1888: pl.77, fig. g) (reproduced in Fig. 10B) exactly. The figure depicts an orange and cream-colored mantle and foot that both are surrounded by colored bands (blue and white). However, we obtained photographs of what is currently being referred to as “Glossodoris cf. cincta” from Mauritius (Fig. 10A), and there is an uncanny resemblance to Bergh’s illustration. We therefore think there is a high probability that the species we have retained the name “Glossodoris sp. cf. cincta” for currently, is something else. The collection of specimens of G. cincta from Mauritius for molecular and morphological analyses is imperative for further resolving the systematics of the Glossodoris cincta species complex. "

and they (https://www.biotaxa.org/Zootaxa/article/view/zootaxa.4444.5.1/33989) conclude:

The present study on Glossodoris and Doriprismatica shows that subtle, but consistent, color pattern differences can be useful in detecting pseudocryptic species. The importance of subtle but differing color patterns being good differentiators of recently diverged pseudocryptic species is similar to the findings of Hoover et al. (2015), Lindsay & Valdés (2016) and Uribe et al. (2017). Clearly, considerable variation in plasticity of color pattern exists in nudibranchs and the degree of polymorphism can be extremely limited or highly variable. The same can also be said for morphological variation of traditional characters such as radular morphology and anatomy of the reproductive system. In this study, there are strong examples such as characteristics of the radula, jaws and buccal secretory glands that clearly differentiate closely related species such as Glossodoris buko and G. pallida. The fact that these characters are more variable in some species and more consistent in others does not mean that they diminish in their taxonomic value. It simply means they should be examined more carefully to fully understand the range of variability and how this variation correlates with geographical and ecological factors. Further studies are needed to focus on the evolutionary drivers of this variation.
Lack of comparative material of Glossodoris cincta from the type locality hampers our ability to fully resolve the taxonomic status of some of the members of this species complex. This is especially true, given that differences in marginal bands of the mantle once thought to be an artifact of Bergh’s original drawing of this species has now been confirmed by photographs of living animals from the Mascarene Islands (Bidgrain 2017, present study). Further study is needed to resolve these remaining issues within this species complex"

SO:
cf cincta is simply that the current G. cincta is probably several species. Given that G. cincta will be the Mauritius form, and all others will possibly require a new name, the use of G. cf cincta on iNaturalist is superfluous. It will be relatively easy to split the species with a simple atlas (except that iNaturalist does not allow marine atlasses at this stage).
I personally dont think the separation of G. sp cf cincta is warranted and it should be sunk into G. cincta.
Esp seen that almost all existing records of G. cincta on iNaturalist are probably G. sp cf cincta anyway.